hlist.h: Add missing stddef.h include for NULL
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1Userspace RCU Implementation
2by Mathieu Desnoyers and Paul E. McKenney
3
4BUILDING
5--------
6
7 ./bootstrap (skip if using tarball)
8 ./configure
9 make
10 make install
11 ldconfig
12
13 Hints: Forcing 32-bit build:
14 * CFLAGS="-m32 -g -O2" ./configure
15
16 Forcing 64-bit build:
17 * CFLAGS="-m64 -g -O2" ./configure
18
19 Forcing a 32-bit build with 386 backward compatibility:
20 * CFLAGS="-m32 -g -O2" ./configure --host=i386-pc-linux-gnu
21
22 Forcing a 32-bit build for Sparcv9 (typical for Sparc v9)
23 * CFLAGS="-m32 -Wa,-Av9a -g -O2" ./configure
24
25ARCHITECTURES SUPPORTED
26-----------------------
27
28Currently, x86 (i386, i486, i586, i686), x86 64-bit, PowerPC 32/64, S390, S390x,
29ARM, Alpha, ia64 and Sparcv9 32/64 are supported. Only tested on Linux so
30far, but should theoretically work on other operating systems.
31
32ARM depends on running a Linux kernel 2.6.15 or better.
33
34The gcc compiler versions 3.3, 3.4, 4.0, 4.1, 4.2, 4.3, 4.4 and 4.5 are
35supported, with the following exceptions:
36
37- gcc 3.3 and 3.4 have a bug that prevents them from generating volatile
38 accesses to offsets in a TLS structure on 32-bit x86. These versions are
39 therefore not compatible with liburcu on x86 32-bit (i386, i486, i586, i686).
40 The problem has been reported to the gcc community:
41 http://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg281255.html
42- gcc 3.3 cannot match the "xchg" instruction on 32-bit x86 build.
43 See: http://kerneltrap.org/node/7507
44- Alpha, ia64 and ARM architectures depend on 4.x gcc with atomic builtins
45 support.
46
47For developers using the git tree:
48
49This source tree is based on the autotools suite from GNU to simplify
50portability. Here are some things you should have on your system in order to
51compile the git repository tree :
52
53- GNU autotools (automake >=1.10, autoconf >=2.50, autoheader >=2.50)
54 (make sure your system wide "automake" points to a recent version!)
55- GNU Libtool >=2.2
56 (for more information, go to http://www.gnu.org/software/autoconf/)
57
58If you get the tree from the repository, you will need to use the "bootstrap"
59script in the root of the tree. It calls all the GNU tools needed to prepare the
60tree configuration.
61
62
63QUICK START GUIDE
64-----------------
65
66Usage of all urcu libraries
67
68 * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible
69 before including the urcu.h or urcu-qsbr.h header. If your application
70 is distributed under another license, function calls will be generated
71 instead of inlines, so your application can link with the library.
72 * Linking with one of the libraries below is always necessary even for
73 LGPL and GPL applications.
74
75Usage of liburcu
76
77 * #include <urcu.h>
78 * Link the application with "-lurcu".
79 * This is the preferred version of the library, in terms of
80 grace-period detection speed, read-side speed and flexibility.
81 Dynamically detects kernel support for sys_membarrier(). Falls back
82 on urcu-mb scheme if support is not present, which has slower
83 read-side.
84
85Usage of liburcu-qsbr
86
87 * #include <urcu-qsbr.h>
88 * Link with "-lurcu-qsbr".
89 * The QSBR flavor of RCU needs to have each reader thread executing
90 rcu_quiescent_state() periodically to progress. rcu_thread_online()
91 and rcu_thread_offline() can be used to mark long periods for which
92 the threads are not active. It provides the fastest read-side at the
93 expense of more intrusiveness in the application code.
94
95Usage of liburcu-mb
96
97 * #include <urcu.h>
98 * Compile any _LGPL_SOURCE code using this library with "-DRCU_MB".
99 * Link with "-lurcu-mb".
100 * This version of the urcu library uses memory barriers on the writer
101 and reader sides. This results in faster grace-period detection, but
102 results in slower reads.
103
104Usage of liburcu-signal
105
106 * #include <urcu.h>
107 * Compile any _LGPL_SOURCE code using this library with "-DRCU_SIGNAL".
108 * Link the application with "-lurcu-signal".
109 * Version of the library that requires a signal, typically SIGUSR1. Can
110 be overridden with -DSIGRCU by modifying Makefile.build.inc.
111
112Usage of liburcu-bp
113
114 * #include <urcu-bp.h>
115 * Link with "-lurcu-bp".
116 * The BP library flavor stands for "bulletproof". It is specifically
117 designed to help tracing library to hook on applications without
118 requiring to modify these applications. rcu_init(),
119 rcu_register_thread() and rcu_unregister_thread() all become nops.
120 The state is dealt with by the library internally at the expense of
121 read-side and write-side performance.
122
123Initialization
124
125 Each thread that has reader critical sections (that uses
126 rcu_read_lock()/rcu_read_unlock() must first register to the URCU
127 library. This is done by calling rcu_register_thread(). Unregistration
128 must be performed before exiting the thread by using
129 rcu_unregister_thread().
130
131Reading
132
133 Reader critical sections must be protected by locating them between
134 calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
135 rcu_dereference() may be called to read an RCU protected pointer.
136
137Writing
138
139 rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
140 After, synchronize_rcu() must be called. When it returns, the old
141 values are not in usage anymore.
142
143Usage of liburcu-defer
144
145 * Follow instructions for either liburcu, liburcu-qsbr,
146 liburcu-mb, liburcu-signal, or liburcu-bp above.
147 The liburcu-defer functionality is pulled into each of
148 those library modules.
149 * Provides defer_rcu() primitive to enqueue delayed callbacks. Queued
150 callbacks are executed in batch periodically after a grace period.
151 Do _not_ use defer_rcu() within a read-side critical section, because
152 it may call synchronize_rcu() if the thread queue is full.
153 This can lead to deadlock or worse.
154 * Requires that rcu_defer_barrier() must be called in library destructor
155 if a library queues callbacks and is expected to be unloaded with
156 dlclose().
157 * Its API is currently experimental. It may change in future library
158 releases.
159
160Usage of urcu-call-rcu
161
162 * Follow instructions for either liburcu, liburcu-qsbr,
163 liburcu-mb, liburcu-signal, or liburcu-bp above.
164 The urcu-call-rcu functionality is provided for each of
165 these library modules.
166 * Provides the call_rcu() primitive to enqueue delayed callbacks
167 in a manner similar to defer_rcu(), but without ever delaying
168 for a grace period. On the other hand, call_rcu()'s best-case
169 overhead is not quite as good as that of defer_rcu().
170 * Provides call_rcu() to allow asynchronous handling of RCU
171 grace periods. A number of additional functions are provided
172 to manage the helper threads used by call_rcu(), but reasonable
173 defaults are used if these additional functions are not invoked.
174 See API.txt for more details.
175
176Being careful with signals
177
178 The liburcu library uses signals internally. The signal handler is
179 registered with the SA_RESTART flag. However, these signals may cause
180 some non-restartable system calls to fail with errno = EINTR. Care
181 should be taken to restart system calls manually if they fail with this
182 error. A list of non-restartable system calls may be found in
183 signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
184 library do not require any signal.
185
186 Read-side critical sections are allowed in a signal handler with
187 liburcu and liburcu-mb. Be careful, however, to disable these signals
188 between thread creation and calls to rcu_register_thread(), because a
189 signal handler nesting on an unregistered thread would not be allowed to
190 call rcu_read_lock().
191
192 Read-side critical sections are _not_ allowed in a signal handler with
193 liburcu-qsbr, unless signals are disabled explicitly around each
194 rcu_quiescent_state() calls, when threads are put offline and around
195 calls to synchronize_rcu(). Even then, we do not recommend it.
196
197Interaction with mutexes
198
199 One must be careful to do not cause deadlocks due to interaction of
200 synchronize_rcu() and RCU read-side with mutexes. If synchronize_rcu()
201 is called with a mutex held, this mutex (or any mutex which has this
202 mutex in its dependency chain) should not be acquired from within a RCU
203 read-side critical section.
204
205 This is especially important to understand in the context of the
206 QSBR flavor: a registered reader thread being "online" by
207 default should be considered as within a RCU read-side critical
208 section unless explicitly put "offline". Therefore, if
209 synchronize_rcu() is called with a mutex held, this mutex, as
210 well as any mutex which has this mutex in its dependency chain
211 should only be taken when the RCU reader thread is "offline"
212 (this can be performed by calling rcu_thread_offline()).
213
214Usage of DEBUG_RCU
215
216 DEBUG_RCU is used to add internal debugging self-checks to the
217 RCU library. This define adds a performance penalty when enabled.
218 Can be enabled by uncommenting the corresponding line in
219 Makefile.build.inc.
220
221Usage of DEBUG_YIELD
222
223 DEBUG_YIELD is used to add random delays in the code for testing
224 purposes.
225
226SMP support
227
228 By default the library is configured to use synchronization primitives
229 adequate for SMP systems. On uniprocessor systems, support for SMP
230 systems can be disabled with:
231
232 ./configure --disable-smp-support
233
234 theoretically yielding slightly better performance.
235
236Interaction with fork()
237
238 Special care must be taken for applications performing fork() without
239 any following exec(). This is caused by the fact that Linux only clones
240 the thread calling fork(), and thus never replicates any of the other
241 parent thread into the child process. Most liburcu implementations
242 require that all registrations (as reader, defer_rcu and call_rcu
243 threads) should be released before a fork() is performed, except for the
244 rather common scenario where fork() is immediately followed by exec() in
245 the child process. The only implementation not subject to that rule is
246 liburcu-bp, which is designed to handle fork() by calling
247 rcu_bp_before_fork, rcu_bp_after_fork_parent and
248 rcu_bp_after_fork_child.
249
250 Applications that use call_rcu() and that fork() without
251 doing an immediate exec() must take special action. The parent
252 must invoke call_rcu_before_fork() before the fork() and
253 call_rcu_after_fork_parent() after the fork(). The child
254 process must invoke call_rcu_after_fork_child().
255 These three APIs are suitable for passing to pthread_atfork().
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